Technical Field
The present invention relates to a resol phenolic resin for a friction material, a method for producing the same, an adhesive for a friction material, and a wet friction plate.
Related Art
A resol phenolic resin is a resin material which is excellent in mechanical characteristics, electrical characteristics, and adhesiveness. For this reason, resol phenolic resins are widely used as a binder resin which is used when producing a friction material such as a clutch or a brake.
Among these, regarding a resol phenolic resin which is used as the binder resin when producing a friction material which is used in an automatic transmission of an automatic transmission vehicle or the like, that is, a wet friction plate, curing characteristics, such as adhesive strength, needs to be improved in order to improve friction characteristics provided in the above-described wet friction plate, and various examinations have been performed thereon in the related art.
Examples of a technique focusing on the improvement of curing characteristics of a resol phenolic resin include the following.
In Japanese Unexamined Patent Publication No. 2014-24881, there is disclosed an adhesive composition containing a resol phenolic resin (A) of which the curing time is short and which has excellent adhesive strength; a polyvinyl butyral resin (B); a polyvalent metal salt (C); and a metal salt of nitrous acid or an ester of nitrous acid (D).
In Japanese Unexamined Patent Publication No. 2006-83892, there is disclosed an adhesive for a wet friction plate containing nitrate or nitric acid and a resol phenolic resin which exhibits excellent adhesive strength.